We show that the globally invasive, human-infectious flatworm, Haplorchis pumilio , possesses the most physically specialized soldier caste yet documented in trematodes. Soldiers occur in colonies infecting the first intermediate host, the freshwater snail Melanoides tuberculata , and are readily distinguishable from immature and mature reproductive worms. Soldiers possess a pharynx five times absolutely larger than those of immature and mature reproductives, lack a germinal mass, and have a different developmental trajectory than reproductives, indicating that H. pumilio soldiers constitute a reproductively sterile physical caste. Neither immature nor mature reproductives showed aggression in in vitro trials, but soldiers readily attacked heterospecific trematodes that coinfect their host. Ecologically, we calculate that H. pumilio caused ~94% of the competitive deaths in the guild of trematodes infecting its host snail in its invasive range in southern California. Despite being a dominant competitor, H. pumilio soldiers did not attack conspecifics from other colonies. All prior reports documenting division of labor and a trematode soldier caste have involved soldiers that may be able to metamorphose to the reproductive stage and have been from nonhuman-infectious marine species; this study provides clear evidence for an obligately sterile trematode soldier, while extending the phenomenon of a trematode soldier caste to freshwater and to an invasive species of global public health concern.

中文翻译：

---

一种侵入性、感染人类的​​扁虫的物理士兵等级在形态上是极端的并且绝对不育


我们发现，具有全球入侵性、可感染人类的​​扁形虫 Haplorchis pumilio 拥有迄今为止在吸虫中记录到的身体最特殊的士兵种姓。士兵出现在感染第一中间宿主淡水蜗牛 Melanoides tuberculata 的群体中，并且很容易与未成熟和成熟的生殖蠕虫区分开来。士兵的咽部绝对比未成熟和成熟繁殖体大五倍，缺乏生发质量，并且具有与繁殖体不同的发育轨迹，表明H. pumilio士兵构成了生殖不育的物理种姓。在体外试验中，未成熟和成熟的繁殖体都没有表现出攻击性，但士兵们很容易攻击共感染宿主的异种吸虫。从生态学角度来看，我们计算出，在南加州的入侵范围内，感染其寄主蜗牛的吸虫群体中，约 94% 的竞争性死亡是由 H. pumilio 造成的。尽管普米利奥人是一个占主导地位的竞争者，但它的士兵并没有攻击来自其他殖民地的同类。之前所有记录劳动分工和吸虫士兵种姓的报告都涉及可能能够变态到生殖阶段并且来自非人类感染性海洋物种的士兵；这项研究为吸虫兵绝对不育提供了明确的证据，同时将吸虫兵种属现象扩展到淡水和全球公共卫生问题的入侵物种。